Intertidal Molluscan Fauna in Mageshima Island

INTERTIDAL MOLLUSCAN FAUNA IN MAGESHIMA ISLAND

著者 "YAMAMOTO Tomoko, ISHIDA So" journal or 南太平洋海域調査研究報告=Occasional papers publication title volume 38 page range 93-95 URL http://hdl.handle.net/10232/9808 南太平洋海域調査研究報告 No．３８（２００３年２月） OCCASIONALINTERTIDAL PAPERS No． MOLLUSCAN３８（February2003） FAUNA IN MAGESHIMA ISLAND ９３

INTERTIDAL MOLLUSCAN FAUNA IN MAGESHIMA ISLAND

Tomoko YAMAMOTO and So ISHIDA

Molluscan fauna of intertidal rocky shores were investigated at Mageshima Island, which is located 12 km west of Tanegashima Island, Kagoshima Prefecture, Japan. Eighty-four species belonging to 31 families were sampled and they included many subtropical species. Some characteristics of this fauna showed that intertidal rocky shores of Mageshima Island were environmentally comparable to cobble shores.

Keywords: Fauna, Intertidal, Mollusca

Introduction

Mageshima Island is located 12 km west of Tanegashima Island and has a 12 km coastline and is 8.5 in surface-area. It is a flat island with a maximum elevation of 71 m. Historically, this island had no residents and was used as a base for fishing or as a farm except from 1951 to 1980, when more than 500 people reclaimed the island and resided to cultivate sugarcane. The coast of the island is known for a good abalone fishery. Therefore, we can expect that this island has a preferable environment for coastal organisms because of very low human impact on intertidal shores and having subtidal shores which can persevere rich abalone resources. There have been some studies dealing with terrestrial flora and fauna of Mageshima Island (SASAKI et al., 1960; NAKAMINE, 1976). One subspecies of sika deer, , was described from this island (KURODA & OKADA, 1950). Flora and fauna were also studied along the coast of the island (ARAKAWA, 1955; TANAKA, 1976; ITONO, 1979), and it has been known to have various algal species including some tropical species (TANAKA, 1950). However, coastal fauna and flora were rarely studied after residents abandoned the island. In this study, we investigated intertidal molluscan fauna on some rocky shores of this island to gain some insight about the coastal fauna and their environmental condition.

Methods

Preliminary surveys were carried out on September 1998 at five shores of Mageshima Island. One person surveyed rocks in the intertidal area for 30 to 60 minutes at each shore during low tide and noted species name. We selected two shores located on the east and west coast of the island based on data from the preliminary survey areas and surveyed again on August 2000. Cross-shore transects were set from the upper to lower reaches of the intertidal zone. All molluscan species along these lines were sampled and fixed in 10% seawater formalin. ９４ Tomoko YAMAMOTO and So ISHIDA

Table 1. List of molluscan species in intertidal rocky shores of Mageshima Island. INTERTIDAL MOLLUSCAN FAUNA IN MAGESHIMA ISLAND ９５

Result and Discussion

A total of 84 species belonging to 31 families were sampled during this survey (Table 1). This number is almost equivalent to the total number of species in nine coasts of the Satsuma Peninsula (YANO, 2001). Since the latter study dealt with an area more than ten times as larger than this study, we can say that Mageshima Island has a more diversified intertidal molluscan fauna than that of the Satsuma Peninsula. Intertidal molluscan fauna in Mageshima Island was also more diversified than that of Chiringashima Island at the mouth of Kagoshima Bay, which is an uninhabited island. The latter has 57 molluscan species including 42 gastropoda. Among 84 molluscan species in Mageshima Island, 61 were gastropoda, while only 17 species of bivalves were sampled. Since most rocky shores of Mageshima Island also had cobble stones, we sampled few settlement species including many intertidal bivalves. Among 61 gastropod species, at least 26 were carnivorous including many subtropical species belonging to Muricidae and Conidae. The ratio of carnivorous species to all gastropod species in Mageshima Island (26 to 61) was almost equivalent to that of the intertidal cobble shores found in Sakurajima Island (7 to 23) (INADOME, 2002). Since a large ratio of carnivorous species are characteristic to molluscan fauna in cobble shores, it can be said that the environmental conditions of intertidal rocky shore in Mageshima Island were intermediate between that of a rocky shore and a cobble shore. Three species of gastropoda ( and ) are reported to be distributed only south of Amami Island. Some other species, e.g., have their northernmost limit of distribution at Tanegashima Island. These species were also sampled from the southern part of the Satsuma Peninsula and thought to be an irregular distribution without any reproductive capacity. In Mageshima Island, they have enough density to have reproductive capacity and to be able to conserve their population.

Acknowledgements

We deeply thank Mr. S. TATSUZAWA for giving us a chance to investigate the uninhabited island. We are also grateful Mr. Gregory NISHIHARA for his kindly corrections on the manuscript.

References

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